I am leaning toward a thyroid issue. I have over my life experienced all that you have discribed. I am 60. Fatique and lack of concentration, etc. I finally was diagnosed with Graves disease after a year of extreme stress.......illness and death in the family. I feel there is ebb and flow to life. I have taken all the B12 sublinqual and royal jelly's and anything I could, in the past to raise my energy levels. Music does as much as aformentioned to help with momentum. I must add here that I am a caregiver to a 31 year old son who requires much. If I have a good day and accomplish many tasks the next 2 or 3 I am exhausted and find myself pushing myself to do things. I just takes all the joy out of living. Good luck!